Conventional motion picture film comprises frames that are commonly displayed sequentially at a frame rate of 24 frames per second (24 fps), or 30 fps, or some other rate. Required special effects may embodied in the displayed film.
Systems (including "telecine" systems) have been developed for converting motion picture film into video signals. These systems generate a video signal from motion picture film images by scanning the film frames sequentially to generate digitized film images. They then convert the digitized images into a video signal having a standard video frame rate (25 video frames per second for PAL video, 29.97 video frames per second for NTSC video, or 30 video frames per second for SMPTE-240M high definition video). Each video frame consists of two fields.
The average luminance level of scanned film images (obtained by scanning motion picture film frames) often undesirably varies from frame to frame due to optical scatter in the lens assembly of the scanning video camera. Some systems for converting motion picture film into video have implemented "flare correction" algorithms to smooth undesired luminance variation between consecutive frames. Conventional flare correction is performed after the film is scanned, but before the scanned analog images are digitized, by applying a lift correction signal to the scanned analog images. The lift correction signal is typically generated as follows. A black reference object is scanned and the average luminance level (an analog voltage) of the resulting analog image is measured. Then, a contrasting object is scanned (typically a white rectangle on a black background) and the average luminance level of the resulting analog image is measured. The lift correction signal is generated to be proportional to the difference between the two measured "average luminance" voltages.
Conventional systems for implementing flare correction typically employ a capacitative integrator to detect analog luminance levels, and then generate a flare correction signal from the output of the capacitative integrator. Due to use of an integrator, this class of conventional analog implementations imposes a significant time delay on the signal being processed.
Until the present invention, no practical technique for digitally implementing flare correction had been developed.